1. Field of the Invention
The present invention relates to a flow cytometer or a cell sorter for biological particles such as cells and/or bacteria. In particular, the present invention relates to an apparatus and a flow cell structure enabling use of a single-use flow cell.
2. Description of the Related Art
A flow cytometer is an apparatus in which a suspension containing particles such as fluorescence-labelled cells and/or bacteria is made to flow in a flow cell, the flow channel is irradiated with light, and scattered light and/or fluorescence generated when the particles pass through the irradiated region is measured, thereby quantifying the sizes of the particles and/or determining the kinds of the particles. Furthermore, a flow cytometer functions as a cell analysis unit for a cell sorter apparatus for sorting cells, etc., according to their kinds.
In a flow cytometer, a laser beam is narrowed down and applied to a flow channel in a flow cell. As the diameter of the beam is smaller, the energy density of the irradiation can be enhanced and the signal strength is thereby increased, enabling enhancement of the detection sensitivity. However, a large difference in signal strength occurs between particles passing through the central portion of the beam and particles passing through the peripheral portion of the beam. In order to prevent occurrence of this difference, it is necessary to perform either of the following: 1) widening of the laser beam to have a width larger than the width of the flow channel; and 2) high-speed sheath flows are provided around a sample flow to limit the portion of the flow channel where the particles pass through to be narrow. The former case has the drawback of the detection sensitivity being lowered as a result of a decrease in the energy density of the irradiation caused due to the widening of the beam. However, in this case, the sheath flows require an amount of liquid larger than that of the sample flow, and thus is conventionally connected to an external tank of several liters or more. Thus, conventionally, it is impossible to replace the entire liquid sending system. As described above, in a flow cytometer including a tank of a large capacity in its liquid sending system, it is impossible to readily replace the entire liquid sending system.
Therefore, methods for enabling use of a single-use flow cell have been proposed. Japanese Patent Laid-Open No. 2004-85323 discloses that a means using a flow caused by a gravity difference occurring due to the difference between surface levels of an introduced fluid for the flow rate of the fluid is provided to a flow cell chip, enabling the entire liquid sending system to be replaced by means of replacement of the chip. However, because of the gravity difference occurring due to a surface level difference of not more than around 1 cm in the chip, a high flow rate can not be provided, requiring one hour or more for measuring a minute sample of around 10 microliters. Japanese Patent Laid-Open No. 2003-302330 discloses a method for providing stable liquid sending by applying the same pressure to two sheath liquid ports and a sample liquid port on the upstream side. However, a problem arises in that where the surface levels of the two sheath liquids are different from each other, the balance of the sheath flows varies.
Where the flow cell to be used is made of quartz, it is not suitable for a single-use one because it is expensive. Meanwhile, methods for manufacturing a micro fluid chip made of a resin have been laid open. Japanese Patent Laid-Open No. 2006-81406 discloses a micro fluid device including a flow channel for polymerase chain reaction, the flow channel being formed by attaching a substrate resin film and an injection-molded resin member having a recess on a surface thereof to each other, or attaching the substrate resin film, a spacer resin film and another substrate resin film to one another in this order.
However, in the case of a flow cell for a flow cytometer in which a laser beam with a high energy density being used, a problem arises in that where an inexpensive transparent resin is used as a material for the flow cell, fluorescence from the material occurs even when visible light with a wavelength of 400 nm or more is applied, resulting in background noise light in fluorescence detection. The existence of this fluorescence causes deterioration of the fluorescence detection sensitivity of the flow cytometer. In the case of a flow cell made of glass, fluorescence occurs with a light having a wavelength shorter than 400 nm.
Furthermore, in an ordinary flow cytometer, a sample liquid is made to flow at a high speed together with a large amount of sheath flows, and thus, a sample liquid, once it is measured, is diluted by the sheath liquid and in addition, is contaminated by another sample liquid, and therefore, in general, the sample liquid is discarded. However, this is a great disadvantage when measuring a precious sample in a small amount.
Therefore, there is a demand for a single-use flow cell enabling easy replacement of a liquid sending system including sample liquid tanks and sheath liquid tanks, liquid sending pipes and a flow cell and not requiring cleansing for each sample replacement.